AbstractThe rapid rise of global temperature that began about 1975 continues at a mean rate of about 0.18°C/decade, with the current annual temperature exceeding +1.25°C relative to 1880-1920. Global temperature has just reached a level similar to the mean level in the prior interglacial (Eemian) period, when sea level was several meters higher than today, and, if it long remains at this level, slow amplifying feedbacks will lead to greater climate change and consequences. The growth rate of climate forcing due to human-caused greenhouse gases (GHGs) increased over 20% in the past decade mainly due to resurging growth of atmospheric CH4, thus making it increasingly difficult to achieve targets such as limiting global warming to 1.5°C or reducing atmospheric CO2 below 350 ppm. Such targets now require “negative emissions”, i.e., extraction of CO2 from the atmosphere. If rapid phasedown of fossil fuel emissions begins soon, most of the necessary CO2 extraction can take place via improved agricultural and forestry practices, including reforestation and steps to improve soil fertility and increase its carbon content. In this case, the magnitude and duration of global temperature excursion above the natural range of the current interglacial (Holocene) could be limited and irreversible climate impacts could be minimized. In contrast, continued high fossil fuel emissions by the current generation would place a burden on young people to undertake massive technological CO2 extraction, if they are to limit climate change. Proposed methods of extraction such as bioenergy with carbon capture and storage (BECCS) or air capture of CO2 imply minimal estimated costs of 104-570 trillion dollars this century, with large risks and uncertain feasibility. Continued high fossil fuel emissions unarguably sentences young people to either a massive, possibly implausible cleanup or growing deleterious climate impacts or both, scenarios that should provide both incentive and obligation for governments to alter energy policies without further delay.

The paper is a very interesting read, focusing on the policies/possibilities/challenges/costs for "saving the climate".On the assumptions and costs for reducing CO2 to 350 ppm in 2100, (lines 708-726, my emphases):

"Now, with assumption that global emissions will be comparable to today’s level through 2020, Figs. 11b and 13b show that 6%/year emissions reduction starting in 2021 leaves a requirement to extract 72 ppm CO2 (153 GtC) from the air during this century. Emission reductions of 3%/year leave a requirement of extracting 112 ppm CO2 (Fig. 13b) by 2100. Constant emissions and +2%/year emissions growth would require extractions of 328 and 768 ppm CO2 to reach 350 ppm in 2100. The lowest cost is for the case of 6%/year emissions reduction. We assume that 100 GtC will be stored in the biosphere via improved agricultural and forestry practices. We do not mean to diminish the magnitude or cost of this task, but we must assume that it will occur if climate change impacts are to be minimized, and further we expect that developed countries will recognize their obligations to provide assistance required to achieve success. The remaining 53 GtC, at the rate $150-350/tC estimated for BECCS and other intensive negative emission technologies (Fig. 3f of Smith et al 2016), would cost $8-18.5 trillion, thus $100-230 billion per year if spread uniformly over 80 years. In contrast, continued high emissions, say between constant emissions and +2%/year, require extraction of 695-1628 GtC, which corresponds to $104-570 trillion dollars or $1.3-7 trillion dollars per year over 80 years. Such extraordinary cost, along with the land area, fertilizer and water requirements (Smith et al 2016) suggest that, rather than the world being able to buy its way out of climate change, continued high emissions may force humanity to largely live with the climatic consequences. "

I can't even imagine how 100 GtC could be stored in the biosphere via improved agricultural and forestry practices in such a relatively short timeframe. It's a lot of land affected, it's a lot of decisions by numerous actors in various levels needed. Meanwhile, we're moving in the opposite direction, of deforestation in the tropics e.g.According to the referenced paper by Smith et al (2016), "The land use intensity of BECCS is quitehigh, with values ranging from ~1–1.7 ha t−1 Ceq yr−1 where forest residues are used as the BE feedstock, ~0.6 ha t−1 Ceq yr−1 for agricultural residues, and 0.1–0.4 ha t−1 Ceq yr−1 when purpose-grown energy crops are used."Smith et al give a figure for the acerage needed to 1-2 G hectares by 2100, or 100 M square km.Seems we'll need several continents to accomplish that.(Africa has e.g. an area of 30 M sq km)This just serves to illustrate the formidable task laid out before the "Younger People".

Those calculations for CO2 extraction by bioenergy with carbon capture and storage (BECCS) presented by Hansen et al in the "Younger Peoples Burden" paper are built on Smith et al (2016), " Biophysical and economic limits to negative CO2 emissions".Total agricultural land area in 2000 was about 5 Gha, with an area of arable and permanent crops of 1.5 Gha. The area for BECCS represents up to 25% of agricultural land, and 25–46%of arable plus permanent crop area. Afforestation and reforestation (AR) up to 20% of total agricultural land, and 21–64% of arable plus permanent crop area. Smith et al: "Thus, the use of BECCS and AR on large areas of productive land is expected to impact the amount of land available for food or other bioenergy production ... which may prove to be a limit to the implementation of BECCS and AR." I guess so... Global population will increase in these coming critical decades by several billion hungry people. These things just don't sum up.

This is something that needs to be integrated with the current solar energy production.... excess solar energy should be used to convert CO2 to elemental carbon for sequestration:

ABSTRACT. With Fe powder as a catalyst, CO2 is completely converted to graphite within 90minutes. The reaction proceeds at 650°C with an excess of H2. The reaction rate is enlarged byforced circulation and by keeping the water vapor pressure very low. The graphite samplesobtained, consisting of 5mg of carbon, almost immediately produce stable 12C- currents of theorder of 20-30µA in the sputter source of a Van de Graaff accelerator. The currents can bemaintained for at least 10 hours and are comparable to those from commercial graphite. Nomemory effects in the preparation system have been observed.

Without having had the time to read the paper you refer to, I would just like to add my two cents… to help you add up the sums:

1) Those hungry billions will have to lead the way by eating a non-meat diet, but still be able to use the rising sea level to catch more fish near shore2) Agriculture, horticulture and reforestation will have to go hand in hand. Planting and growing stuff in several layers is often called Permaculture3) The basis for our survival will have to be non-food residues incl. wood chips for pyrolytic gasification, and then bury the charcoal to help soils improve their water holding capacity as well as restore their nutrient and carbon balances.

With weather and climate extremes - like the ones we just saw - whether it is in Columbia (five years of drought and a few days of rain from hurricane Matthew), or in Massachusetts (five weeks of drought and a few days of rain from hurricane Matthew), there is no other way to go.

Thanks for your reply, P-maker.I understand what's needed, but I just don't see any of it happening in the coming, critical decades.

My point is that what Hansen et al, Smith et al, etc, suggest, requires fundamental changes in people's behavior. But behaviors aren't easily changed. Most worrying is what's going on in the developing countries, in India, S.E.Asia, Africa, those regions where very strong population growth and economic growth are expected in the coming 20-40 years. There is certainly no place for BECCS or AR etc. in those parts of the world. There will be no reforestation, but probably continued deforestation due to population pressure.

When people become more affluent, their behavioral pattern is to consume more, to travel more etc. And regarding food, they typically eat more meat, and less vegetables, - there are several references to research showing that on the forum. If you want to change policies you can do that only if there is popular support - absent authoritarian climate-saving regimes, which I think will not be realized within at least 50 years. Yes, you can tax people out of using FF (carbon tax), or out of eating meat, etc. But you need the popular support to do it, and some degree of international cooperation. And I just don't see those things happening when people's mindsets are tuned into consumption. And specifically, in the 3d world, there is a strong urge to catch up, to raise living standards in the short run. All focus is on the current generation. For the future, you raise kids, and then they will solve their problems.

My conclusion is that the policies discussed by Hansen, by Smith etc., are totally unrealistic scenarios. Nothing will happen that quick in the world as we know it. We are more or less certain to pass some tipping points where slow feedback processes become so strong that we'll lose control. Costs will not be the estimated $104-570 trillion dollars for a more or less controlled path, but much higher the longer we wait, and eventually they will be prohibitively high. BECCS, AR etc. might be implemented, but it will be too slow, too little, too late, and it won't stop the runaway climactic changes.

Very good (and depressing) paper by Hansen, although most of the key ingredients were known already.I read his message as - if you blindly trust in Carbon extraction to get humanity out of the trap, don't. It'll be too expensive and therefore unfeasible.He probably hopes that this message might convince some people to act now rather than postpone treatment.

Their summary:In December 2015, member states of the United Nations Framework Convention on Climate Change (UNFCCC) adopted the Paris Agreement, which aims to hold the increase in the global average temperature to below 2°C and to pursue efforts to limit the temperature increase to 1.5°C. The Paris Agreement requires that anthropogenic greenhouse gas emission sources and sinks are balanced by the second half of this century. Because some nonzero sources are unavoidable, this leads to the abstract concept of “negative emissions,” the removal of carbon dioxide (CO2) from the atmosphere through technical means. The Integrated Assessment Models (IAMs) informing policy-makers assume the large-scale use of negative-emission technologies. If we rely on these and they are not deployed or are unsuccessful at removing CO2 from the atmosphere at the levels assumed, society will be locked into a high-temperature pathway.

The issue is rate-of-change, the slogan "carbon budget" is like "manifest destiny" and the genocide this time global.

Rate-of-change has today put all of the Beaufort Sea at the aragonite saturation point and all Alaskan water will be below that within 60-years good bye fisheries, eh?

The Miocene was warmer & CO2 higher than the Pliocene that was warmer & CO2 higher than the Quaternary's ice-ages that didn't occur before the final step when the Isthmus of Panama filling allowed geophysically for them to happen

The Southern Ocean opening up preceding this gave Antarctica the beginnings of an ice-sheet.

That was say 2.5-million years ago & the initial "ice-age" was a cooling, the first ones until about 1.5-Mya on the 41k cycle when the 100k Milankovich cycle began having effects.

So, during the last half of the Pleistocene CO2 didn't go above 305±5-ppm that 3 interglacials back, 320k-years ago, our interglacial ends in ~1,500-years the planet on a cooling trend before emissions changed that. [people.clas.ufl.edu/jetc/files/Tzedakis-et-al-2012.pdf]

This is acidifying the oceans heavily to effect phytoplankton, the basis of the oceanic food-chain : "The rate of acidification is 10-times faster or more than anything we have seen for the past 50-million years and perhaps over the last 300-million years."ICES ASC 2013 Plenary Lecture, 9:10 into 1:01:08;

Now consider the wisdom of charging a CARBON FEE, not a tax the huge difference is the money goes equally to society to spend as it wants this time not what Team Oligarch wants to fake doing something about the emissions with the money, eh?

We must exit the Steam Age for electrons, most grid power is for thermal end-use 80%, not electricity 20%, so to switch will only take 5-years moving to solar-HVAC+hot-water, maybe 2-months if it was a war, don't tell ?

Tim, Thanks for giving ocean acidification a bump on the forum today. Both the PMEL and UW are close to where you live and therefor you have an opportunity to attend public forums on the subject. I was fortunate to see Richard Zeebe give a talk at the " Oceans in a High CO2 " symposium in 2012 so I was happy to view the Zeebe talk you linked today. It appears the upward shift in climate sensitivity due to slow feedbacks will result in a very long duration to our initial fossil carbon inputs. Permafrost thaw and methane hydrates will IMO give our initial fossil fuel carbon inputs a very long impact on this planet. Waiting to develop or depending upon carbon capture to fix our cascading carbon issues must carefully ignore the threat these slow feedbacks entail. Ocean acidification is a young field of research and you have an opportunity to influence public assimilation of it's implications should you chose to do so. Washington State is probably the front runner in both research institutions and locally documented effects for O/A. The Puget Sound is annually extremely effected by acidification.

Then another recent flash was California and others going full-on for desalinization and I want to set up a delivery system for their waste salts to put back in the ocean to raise alkalinity. A shellfish hatchery went in and they are losing 4-5 months a year already to there runoff freshening the water more than upwelling.

"ARCUS D.C. Arctic Research Seminar Series - 31 March 2016";55:33;

We must do things at scale or those fisheries are gone within 60-years.

Then, I do have a thread on ARS to dam Bering Straits to create a sea-ice refuge to hold ice all year. Briefly it's Dutch methods revised for deeper water, learning & refining the idea by restoring and raising the villages being lost to erosion until ready.

Then to build a weir dam at St. Lawrence Island with the locks for shipping east end to fit with sea-mammal migrations and with levees & artificial shoals keep the freshwater & shipping near shore, eventually for the entire Arctic Ocean to prevent early melt-out to-sea.

With the dam in restricting Pacific water to 1/100th the volume and the 30-Twh/year in heat transport it brought in to put in ice-polders to quiet the water and current to refreeze the bottom.

If that works to take back over the Chukchi and at least half the Bering Sea with them.

And, to build atolls around the large methane flares growing in the shallow continental shelf areas to refreeze those, they may freeze fast from the bubbles creating an up current pulling colder water down around the sides.

As a geophysical solution having a cold forcing globally from it being in the Arctic not tied to emissions to work, it makes thermal sense to try.

It hasn't been modeled my dime yet do have a conference with Cray first week in December to discuss it as a final goal starting with a hovering propeller design with a very new flow regime it's tiny and "cheap" for them to optimize it to gain funding.

“Abstract. Global temperature is a fundamental climate metric highly correlated with sea level, which implies that keeping shorelines near their present location requires keeping global temperature within or close to its preindustrial Holocene range. However, global temperature excluding short-term variability now exceeds +1 °C relative to the 1880–1920 mean and annual 2016 global temperature was almost +1.3 °C. We show that global temperature has risen well out of the Holocene range and Earth is now as warm as it was during the prior (Eemian) interglacial period, when sea level reached 6–9 m higher than today. Further, Earth is out of energy balance with present atmospheric composition, implying that more warming is in the pipeline, and we show that the growth rate of greenhouse gas climate forcing has accelerated markedly in the past decade. The rapidity of ice sheet and sea level response to global temperature is difficult to predict, but is dependent on the magnitude of warming. Targets for limiting global warming thus, at minimum, should aim to avoid leaving global temperature at Eemian or higher levels for centuries. Such targets now require negative emissions, i.e., extraction of CO2 from the air. If phasedown of fossil fuel emissions begins soon, improved agricultural and forestry practices, including reforestation and steps to improve soil fertility and increase its carbon content, may provide much of the necessary CO2 extraction. In that case, the magnitude and duration of global temperature excursion above the natural range of the current interglacial (Holocene) could be limited and irreversible climate impacts could be minimized. In contrast, continued high fossil fuel emissions today place a burden on young people to undertake massive technological CO2 extraction if they are to limit climate change and its consequences. Proposed methods of extraction such as bioenergy with carbon capture and storage (BECCS) or air capture of CO2 have minimal estimated costs of USD 89–535 trillion this century and also have large risks and uncertain feasibility. Continued high fossil fuel emissions unarguably sentences young people to either a massive, implausible cleanup or growing deleterious climate impacts or both.”